According to the known state of the art, the raw material components for producing glass and the refining materials are mixed with one another in the proportions necessary for the desired type of glass and are introduced into a melting end of the furnace in which they are melted as a result of the supply of heat, especially by means of burners located above the melting end, and in which Cthe necessary degassing of the melt, the so-called refining, is also carried out.
To reduce the outlay of energy required for the melting operation, it is known to introduce the mixture of raw material components into the melting end in a preheated or heated state. Since the melting end may have a depth of 0.9 m to 1.4 m, a very high outlay of energy is necessary to ensure that the raw material components are melted down completely. Furthermore, very different temperature conditions arise in the melting end. Thus, the melt has a lower temperature in the regions of the walls of the melting end than in the central region thereof. Since this in particular causes difficulties in homogenizing the melt, an exceptional outlay in terms of technology and time is required to degas completely not only the layers of melt which lie at the surface, but also the layers lying below the surface, especially those lying near the bottom of the melting end. This is because the glass bubbles contained in the molten masses located in the lower region of the furnace do not have the necessary kinetic energy available to reach the surface. To ensure that the raw material components are melted down and that the melt is refined, it is therefore necessary for the melt to remain in the melting end for a relatively long time.
The known production processes are also disadvantageous because the fine distribution appropriate to the glass batch composition, which can be achieved by mixing all the raw material components in a mixer, with correct proportions of components in each mixing batch is not necessarily present when the mixer is emptied. Since segregation can occur, this fine distribution does not take place even during subsequent transport into a supply vessel for feeding the melting end. Consequently, the distribution of raw materials can be heterogeneous even when the mixture of raw material components is introduced into a melting end in thin layers. As a result, the filling layers fall to different depths depending on the thermal gradients. Masses of different viscosities impede one another and cause convection currents which, after lengthy circulation of the layers, though helping gradually to melt them down, nevertheless contribute little to the homogenization necessary for achieving the required glass quality. Consequently, the known balance reactions between the raw material components proceed very slowly because they cannot be controlled.
Because of the large-volume design of conventional melting ends, and also because of regenerators, underfloor channels, reversing devices and recuperators of corresponding dimensions, which are arranged on statically calculated supporting structures, the melting ends are, on the one hand, extremely costly and must, on the other hand, be designed to be fixed in place as a result of their great weight and the abovementioned design. In addition, since any production of other glass products necessitates a further identical or similar glass tank, this often causes excess capacity.
Moreover, shutting down melting furnaces causes damage, and high energy costs are incurred by keeping them in operation. In glass furnaces predominantly heated by fossil fuels, the necessary outlay of energy increases sharply because of arching as a result of high radiation losses and because of the need for a greater supply of heat to the molten mass. This increased outlay of energy is required even when the batch is preheated and costly insulation is provided.
It is known from German Patent Specification No. 2,518,635 to apply the raw material components in thin layers onto the glass melt located in a melting furnace. However, even in this case, because of the large volume of the melting end, high temperature gradients arise, and these bring about convection currents causing uncontrollable migration of the layers, as a result of which the melt provided for processing is defective. Because of the very long retention time in the furnace, increases in output can be achieved only by enlarging the installation.